You've left your actual question blank, and not said whether you're asking about PAYG or pay-monthly.... So I'll answer for both
Pay-monthly phones will remain active for as long as the bills are being paid, it matters not one jot whether it's being used or not. If the bills aren't paid, then the debt collections process (known as "collections") kicks in
PAYG phones are subject to the hibernation policy which requires chargeable usage at least once every 179 days to avoid suspension, Details are at https://community.ee.co.uk/t5/Pay-as-you-go/What-is-pay-as-you-go-and-flex-hibernation-and-how-do-I-...
